Work on this project progresses along similar lines to that accomplished in 1974-75. Our collaboration with the Oregon State Health Department was continued and 3 strains of Colorado tick fever virus were recovered from Dermacentor andersoni. More significantly, 2 additional strains of Rocky Mountain spotted fever group rickettsia were isolated in Vero cells from Ixodes pacificus. Evidence of rickettsiae was demonstrated in 7 pools of I. pacificus examined by immunofluorescent techniques. Numerous isolations of virus were made from Ornithodoros capensis during the past year. Specifically, 2 isolates of a virus closely related to Hughes virus were recovered from O. capensis collected on Aves Island in the Carribean; 63 strains of Soldado virus were recovered from O. capensis ticks collected from the Great Barrier Reef near Australia. This Upolo-like agent has been characterized and is ready to be described and reported.